/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    bool hasCycle(ListNode *head) 
    {
        ListNode* fast=head;ListNode*slow=head;
        while(fast)
        {
            fast=fast->next; if(fast==NULL) break;
            fast=fast->next;
            slow=slow->next;
            if(fast==slow) return true;
        }    
        return false;
    }
};
